The purpose of this research study is to gain a better understanding of the changes that may occur in the breast when a woman uses an oral contraceptive (birth control pill). Some research indicates that women who use birth control pills with lower amounts of estrogen (a hormone in the birth control pill) may have lower breast cell growth than women who use birth control pills with a higher amount of estrogen; this research will examine that in detail. This research will also test whether the results found in HS-07-00269 can be confirmed.